FAR-ULTRAVIOLET OBSERVATIONS OF COMET C/2001 Q4 (NEAT) WITH FIMS/SPEAR

Abstract

We present the results of far-ultraviolet observations of comet C/2001 Q4 (NEAT) that were made with the Far-Ultraviolet Imaging Spectrograph on board the Korean satellite STSAT-1. The observations were conducted in two campaigns during its perihelion approach between 2004 May 8 and 15. Based on the scanning mode observations in the wavelength band of 1400-1700 angstrom, we have constructed an image of the comet with an angular size of 5 degrees x 5 degrees, which corresponds to the central coma region. Several important fluorescence emission lines were detected including S I multiplets at 1429 and 1479 angstrom, C I multiplets at 1561 and 1657 angstrom, and the CO A(1)Pi-X-1 Sigma(+) Fourth Positive system; we have estimated the production rates of the corresponding species from the fluxes of these emission lines. The estimated production rate of CO was Q(CO) = (2.65 +/- 0.63) x 10(28) s(-1), which is 6.2%-7.4% of the water production rate and is consistent with earlier predictions. The average carbon production rate was estimated to be Q(C) = similar to 1.59 x 10(28) S-1, which is similar to 60% of the CO production rate. However, the observed carbon profile was steeper than that predicted using the two-component Haser model in the inner coma region, while it was consistent with the model in the outer region. The average sulfur production rate was Q(S) = (4.03 +/- 1.03) x 10(27) s(-1) which corresponds to similar to 1% of the water production rate.